IDENTIFICATION AND QUANTIFICATION OF INTRINSIC OPTICAL CONTRAST FOR NEAR-INFRARED MAMMOGRAPHY

Near-infrared spectroscopy has been used to quantify the composition o f healthy female breast tissue in vivo, By collecting transilluminatio n spectra in the wavelength range 680-1100 nm at 7-9 positions on the breasts of five female volunteers, an attempt was made to quantify the intra-and intersubject variability of breast composition. The dominan t absorbers are water, lipids and hemoglobin. Hemoglobin concentration in the breast is substantially lower than that in the brain or muscle (less than 10 mu M). The measured deoxyhemoglobin concentration can v ary by up to 100% between different positions on the same breast. Wate r and lipid concentrations can show similar variability. Phantom and s imulation studies demonstrate that this variability is not due to the effects of tissue boundaries on the measurements. The low hemoglobin c oncentration implies that optical breast imaging should be performed a t wavelengths below about 850 nm to ensure that the image contrast com es predominantly from hemoglobin. Intrasubject variability could have implications for the ability of optical imaging to discern tumors from background contrast variations.